Does Blender consider each frame to be separate scenes, while rendering animation?
I can only answer the first question.

Each frame is NOT considered a different scene. Every scene has their own frames/timeline.

So "Scene 1" could have 250 frames, and "Scene 2" could have 150 frames. However, the first 150 frames in each of these scenes are different. Changing some animation in frame 50 in "Scene 1" does not affect frame 50 in "Scene 2" (unless you've specifically linked them).

At the top of Blender, you can see which scene you currently reside in: